Effect of particle-particle collision in decaying homogeneous and isotropic turbulence.

The effect of particle-particle collision in decaying homogeneous and isotropic turbulence in the absence of gravity is studied using direct numerical simulation. The objective is to verify the relative importance of the particle-particle collision effect on particle distribution and other characteristics in gas-solid flows with transition from dilute to dense flow. A pseudospectral method coupling with a discrete element method (a hard-sphere approach) is used to simulate the gas turbulence and particle-particle collision dynamics. The effects of particle-particle collisions with different Stokes numbers and mass loadings are investigated. Suggestions for the consideration of the particle-particle collision effect in transition from dilute to dense gas-particle flow are provided. An empirical criterion for demarcation of dilute and dense flow is established. A selective effect of particle-particle collision on particle distribution with particle Stokes numbers higher and lower than unity is found and qualitatively demonstrated.